BCAB #1953 - Protection from Precipitation in an Alteration to an Existing Building

February 6, 2025

Re:  Protection from Precipitation in an Alteration to an Existing Building

Project Description

The project is the alteration of an existing single-family residence to include a secondary suite.  The building was constructed in 1996 and the stucco exterior cladding system does not include a drained and vented capillary break (i.e., rainscreen).

As part of the project, an existing exterior stair was rebuilt with cast-in-place concrete to meet egress requirements for the new dwelling unit.  Portions of the concrete stair and its landings have been cast directly against the existing stucco cladding on the existing exterior wood-framed wall.

The stair treads have a 2% downslope and 1% cross slope so that no water stands or pools against the wall.

Applicable Code requirements (BCBC 2024)

Sentence 1.1.1.2.(1), Division A, Application to Existing Buildings

(1) Where a building is altered, rehabilitated, renovated or repaired, or there is a change in occupancy, the level of life safety and building performance shall not be decreased below a level that already exists. (See Note A-1.1.1.2.(1).)

Sentence 9.27.2.1.(1), Division B, Minimizing and Preventing Ingress and Damage

(1) Except where exterior walls are protected from precipitation or where it can be shown that precipitation ingress will not adversely affect occupant health or safety, exterior walls shall be designed and constructed to

(a) minimize the ingress of precipitation into the assembly, and

(b) prevent the ingress of precipitation into interior space.

(See Note A-9.27.2.1.(1).)

Decision being appealed (Local Authority’s position)

The new stairs poured against the stucco have decreased the building performance because the exterior wall is no longer able to shed water as designed and will be susceptible to water pooling and ingress from lack of drainage and airflow.  The stairs must be altered so that the wood framing will not be adversely affected by any precipitation and the performance of the existing wall will not be reduced below that which was previously existing.

Appellant's position

The new concrete stair will trap no more moisture than the existing concrete-based stucco which is applied directly to the sheathing.  The wall system will perform as it has from the time it was installed.  There is no evidence that the wall system will see more exposure to water than before.

Appeal Board Decision #1953

The Board confirms the decision of the local authority.

It is the determination of the Board that the installation of the new concrete stair will result in a decrease in the performance of the existing building envelope.  The installation must be altered so that the performance of the existing building envelope is not decreased below the level that already exists.

Reason for decision

The existing building envelope system relies on water shedding and drying to perform its intended function.  The installation of the concrete stairs decreases the ability for portions of the building envelope system to perform as intended. 

Don Pedde
Chair, Building Code Appeal Board